This invention relates to a water-soluble and edible protein derived from keratin and to a process for preparing said protein from sources of keratin such as animal hair, fur, feather, wool, hooves, horns, claws, shells, nails and keratinous materials such as meals prepared from them.
While solutions of proteins have been prepared from such sources in the past, the protein has usually been so degraded or contaminated that it has been unsatisfactory for use as a food and for many other uses.
A keratin is a hard, insoluble, fibrous protein, the amino acid content and sequence of which may vary slightly depending upon the animal structure in which it occurs. The keratins are distinguished from other structural proteins such as silk, fibrin, collagen and muscle proteins by their amino acid composition and particularly by the large number of cystine units in the keratin molecule. The hardness and insolubility of keratins is attributed to the intermolecular cross-linking of the peptide chains by these cystine units. It is apparent that a soluble protein derived from a keratin can no longer be called a keratin so, for want of a better name, the water-soluble, edible, substantially odorless, free-flowing, cream-colored flour obtained from the process of this invention is called herein a keratinaceous protein.
Prior to the discovery of the invention disclosed and claimed herein, there has not been, to the applicants' knowledge, a practical method for preparing from such sources a keratinaceous protein which is substantially non-degraded and which is substantially completely water-soluble and digestible by animals. While the preparation of feather meal and horn meal has been known for many years, these products are substantially insoluble in water. Methods for preparing such meals are taught in U.S. Pat. Nos. 2,170,562; 2,702,245; 3,464,342 and 3,617,313. It has been generally accepted that the hydrolysis of keratin to produce a water-soluble protein is feasible only when catalyzed by an acid, a base or some special chemical agent.
The patent literature teaches many variations of such hydrolytic procedures and it may be represented fairly by U.S. Pat. Nos. 926,999; 2,137,365; 2,158,499; 2,474,339; 2,597,566; 3,464,825; and 3,806,501.
The cooking of animal fats, meat scrap, offal and slaughter house wastes with steam at from 50 to 120 p.s.i.g. for from 10 to 30 minutes is taught as a rendering process for the recovery of tallow and a high protein meal in U.S. Pat. Nos. 3,263,592 and 3,295,982. An aqueous protein referred to as stickwater in these patents is a by-product of said rendering process. It is not clear from the teachings in these patents whether this aqueous protein is a suspension or a solution, nor is it clear whence said protein came. The histones present in the animal tissue and the blood proteins are the more apparent sources.
It has been noted by R. Renner et al at page 582, Volume 32 of Poultry Science that the addition to soybean meal of up to an equal weight of water partially prevents the loss of nutritive value of the meal caused by excessive heating during processing. It has remained for the applicants to discover, however, that the non-catalyzed hydrolysis of keratins in the presence of a large amount of liquid water gives high yields of a soluble protein.